This invention relates to fluid gages and meters and in particular sensors for indicating when dispensing machines such as soft drink dispensers have run out of one or more of the syrup, carbonated water, or other ingredients used in the machine.
In the past soft drink and other dispensers have used a number of sensing mechanisms for determining when syrup and carbonated water reservoirs have been emptied. These sensors have included float type tank gages having a flotation device connected to a stationary pivot point and initiating an electrical signal when the float has fallen to the bottom of the tank. This type of fluid supply sensor, however, has proven unsatisfactory for soft drink dispensers and vending machines. These dispensers handle a variety of syrups and other sugar products, which tend to build up coatings on the walls of the tanks and on the float sensor over a period of time. Such coatings alter the operational characteristics of the float level indicator which becomes more sluggish with time. Very often electrical contacts associated therewith also become coated rendering the sensor inoperative. Under such conditions the sensor will either indicate that the machine is out of syrup or will indicate a constantly full condition even after an emptying has occurred.
Another type of sensor used to indicate the presence or absence of fluid from a storage tank is an electrically conductive electrode pair. This type of sensor comprises a pair of electrodes which are inserted into the storage tank from the top, protruding to a point in close proximity but not touching the bottom of the tank. A very mild electric current is passed between the two electrodes and will continue to be conducted until the fluid within the tank has been completely emptied. When this fluid has been completely emptied the electrical current activities between the two electrodes are eliminated, indicating an empty tank. This indicator also may take a second form having pair of small rectangular or circular electrodes, mounted by means of an insulator to opposing walls of the tank near the bottom of the tank. As with the rod type electrodes described above, these electrodes pass a very mild current between themselves when a fluid level permits condition.
Level indicators as these tend to build up coatings of syrup or other materials on their surfaces. As this coating builds up, the electrical activity between the electrodes diminishes.
These prior art syrup level sensors have to be cleaned periodically in order to function properly, requiring regular servicing of the machine and increasing the operating cost per machine. It is desirable therefore to develop a tank sensor which does not require cleaning and regular servicing.
An object of this invention is to provide a "tank-empty" sensor which determines when a tank has been emptied of syrup or other fluid normally held there-within.
A second object of this invention is to provide such a sensor which need not be inserted into the syrup tank and which need not come in direct contact with the syrup held therewithin.
A further object of this invention is to provide such a sensor including circuitry for initiating an empty tank alarm and for activating controls to apparatus associated with the tank, for altering the operation of that apparatus as a function of the empty tank.